Facet tooth



Aug. '7, 192a.

' H. STAHL FACE? TOOTH Filed March 12, 1926 Bush-("orb fitter-nay Patented Aug. 7, 1928. r

. UNITED STATES HANS STAHL, OF EISLEBEN, GERMANY.

FACET TOOTH.

Application filed March 12, 1926, Serial No. 94,108, and in Germany March 17, 1925. i

This invention relates to a facet tooth of that type in which in the rear side of the tooth an undercut cavity is arranged designed to receive a correspondingly shaped projection on the backing, the tooth being fixed in this position by the filling of the cavity with a mass capable of solidifying rapidly. In facet teeth of this type the undercut cavity of the tooth is usually arranged and shaped so that the teeth are fitted over the projection on the backplate in the direction of the biting edge of the tooth towards the maxilla. This presents the inconvenience, that no protection for the biting edge can be provided as the manner of mounting the toot-h on the back plate does not permit of fixing such a protection. Artificial teeth without protecting plate are, moreover, subject to the liability of the unprotected biting edge being easily broken.

In ordinary tooth facets the rear face of the cavity for the projection is parallel to the rear face of the facet and to the front side of the backing plate. The facet is consequently not held very securely upon the projection as the undercut-ting of the sides cannot be very great owing to the shallowness of the facet. The delicate undercut edges of the facet are therefore liable to break off easily if the backing plate is moved even slightly. This danger is all the greater as the back plate must be thin, owingto the sharp counter-bite, and is consequently very resilient.

To avoid these inconveniences the cavity in the rear face of the tooth facet is, according to the invention, of such shape that it is open in the direction of the cutting edge of the tooth so that it can be pushed from the cutting edge overthe correspondingly shaped nipple on the back plate. T he undercut side walls of the cavity are of trapezoidal-or wedge-shape with regard to one another so that they are closer toget-her at the closed end of the cavity than at the open end. The cavity for the nipple if of such shape that not only the sides of the same extend wedge-shaped, but also the inner side or back face of the cavity is inclined with regard to the rear side of the facet or with regard to the front side of the plate in the direction of pushing on, e. g. in the direction of the pressure exerted during mastication, so that the undercut side edges of the cavity are thinner at the open end of the cavity than at the opposite end of the same, wherefroin result the advantages that, on the one hand, the facet can yield without breaking under the masticating pressure as the backplate of metal is more elastic than the porcelain facet of the tooth, and, on the other hand, that the undercutting in the thicker portion of the tooth is deeper so that the undercut side edges of the cavity, liable to break off easily, are as thick as the thickness of the body of the tooth allows.

In tooth facets of known type, if the tooth 1s to be pushed over the nipple from the neck end, the wedgeshaped section of the cavity extends over the entire length of the tooth whilst, according to the invention, the cavity 18 closed at the end opposite the end from which it is pushed over the nipple so that, in combination with the bent extension of the protecting plate underneath the tooth, a mounting from above and from below for the portion of the body of the facet is obtained which limits the cavity at the lower end, the tooth being thus elasticically suspended on the back plate so that the tooth can give way in the direction of the masticating pressure. In this form of construction the cementing serves mainly for filling the fine joints.

An embodiment of the invention is illustrated, by way of example, in the accompanying drawing in which Fig. 1 shows in side elevation an incisor facet, the back plate being shown in section.

Fig. 2 is a rear elevation of the facet of the tooth.

Fig. 3 is a longitudinal section on line 33 of Fig. 2. i

Fig. 4: is a cross section on line 4tt of Fig. 1.

The tooth facet 1 has the usual outer shape and it is bevelled at the cutting edge on the inner side to fit onto the protection 2 on the back plate 3.

The cavity 4; in the rear face of the tooth facet is enlarged and open at the cutting edge, the undercut side edges 5, 6 being from this open end inclined the one towards the other so that the cavity as well as the nipples 7 on the back plate 3 are wedge-shaped. The rear face 9 of the cavity is inclined with regard to the rear face of the body of the tooth, so that the undercut side edges 5, 6 of the cavity are thicker at the closed end of the cavity than at the open end of the same.

The tooth facet is pushed over the wedgeshaped undercut nipple 7 on the back plate llu 3 from the neck end, e. g. the cutting edge in front, until the cutting edge comes in contact with the protection 2 and the undercut inclined side edges of the cavity are closely in contact with the undercut inclined side edges of the nipple. This is easily obtained by retouching the side edges of the nipple on the back plate. The Wedge shape of the nipple T on the back-plate and the wedge shape of the cavity 4 in the tooth, seen in the cross section on line 33 of Fig. 2,- have the effect that the tooth, when being pushed onto the nipple, is strongly pulled against the back plate. The fine joints between the tooth facet l and the back plate 3 and the free spaces in the cavity are subsequently filled by cementing or otherwise. The facet is further secured in its position by the extension 8 of the back plate 3 which is bent so that it grips over the corresponding edge of the tooth facet 1. This is not necessary for pin teeth as the facet bears on the root of the tooth.

If india rubber is used as material it is merely necessary to fix the facet on the protecting plate by cementing as the india rubher is then worked in under the facet.

A special advantage of the invention is, that the facet permits of strongly moulding the protecting plate, the biting action being then especially strong.

I claim An artificial tooth comprising a facing having an incisal edge inclined toward its lingual face and having a dove-tailed recess opening through its incisal edge and lingual face and term nating inwardly of its gingival edge, said recess being of double-wedge formation in the directions from. front to rear and from side to side of the tooth, said recess being of maximum width and minimum depth at its end opening through the incisal edge of the facing and thence decreasing in width and increasing in depth toward and being. of minimum width and maximum depth at itsend adjacent the gingival edge of the facing, and said recess having its inner wall inclined with relation to the labial face of the facing and having its side walls inclined to the plane of the longitudinal center of the facing and converging toward the lingual face of the facing and its inner end wall inclined in the direction of the gingival edge and labial face of the facing. and a backing plate having a dovetailed projection of a form corresponding to and adapted to fit within said recess of the facing and provided with an inclined projection lapping over upon the incisal edge of the facing In testimony whereof I affix my signature.

HANS 'STAHL. 

